Definition and Position in the Copper Family
Thick-walled copper tube and thick-walled brass tube describe seamless tube whose wall thickness is deliberately greater than the minimum needed to carry the design pressure. Heavy walls are specified for three reasons: to withstand high working pressure with a safety margin, to provide sacrificial metal where erosion or corrosion allowance is required, and to leave enough material for machining threads, grooves or bearing surfaces.
Copper tube covers the unalloyed grades discussed elsewhere in the copper range, while brass tube is a copper-zinc alloy. Brass is stronger and harder than pure copper, machines far more freely, and costs less per kilogram, which is why heavy-wall tube in the lower-pressure and higher-wear duties is usually brass rather than copper. Copper remains the choice where maximum thermal or electrical conductivity is the dominant requirement.
Grade Selection and Standards
| Grade / UNS | Family | Nominal composition | Character | Typical standard |
|---|---|---|---|---|
| C26000 | Cartridge brass | Cu 68.5–71.5 %, Zn balance | Excellent cold formability, good strength | ASTM B135, EN 12449 |
| C27000 | Yellow brass | Cu 63.0–68.5 %, Zn balance | Higher strength, moderate ductility | ASTM B135, EN 12449 |
| C28000 | Muntz metal | Cu 59.0–63.0 %, Zn balance | High strength, hot working grade | ASTM B135, EN 12449 |
| C36000 | Free-cutting brass | Cu 60.0–63.0 %, Zn balance, Pb 2.5–3.7 % | Best machinability | ASTM B16, EN 12164 |
| C11000 | ETP copper | Cu 99.90 % min | Highest conductivity, soft | ASTM B75, EN 12449 |
| C12200 | DHP copper | Cu 99.90 % min, P 0.015–0.040 % | Welding grade copper | ASTM B75, ASTM B88 |
Product standards for seamless tube are ASTM B135 for brass tube in general engineering service, ASTM B111 for copper-alloy condenser and heat-exchanger tube, EN 12449 for seamless round copper and copper-alloy tube in metric sizes, GB/T 1527 for Chinese drawn copper tube and JIS H3300 in Japan. Where a pressure vessel or pipeline code governs the installation, the design wall thickness is calculated in accordance with that code and the ordered wall is the next heavier commercially available size.
Wall Thickness, Pressure Rating and Tolerances
Heavy-wall tube is normally ordered by outside diameter and wall thickness rather than by gauge or by nominal bore. For a given diameter, the pressure capability rises almost linearly with wall thickness, while the outside diameter stays constant so that existing fittings and threads continue to suit.
| Outside diameter range | Wall thickness range | Supply length | Typical use |
|---|---|---|---|
| 6 mm – 25 mm | 1.0 mm – 3.0 mm | Straight 3 m / 6 m or coil | Instrumentation, hydraulics, gas lines |
| 25 mm – 76 mm | 2.0 mm – 8.0 mm | Straight 3 m / 6 m | Process piping, heat exchangers, bearings |
| 76 mm – 219 mm | 4.0 mm – 25 mm | Straight up to 6 m | Bus pipe, condensers, heavy-duty sleeves |
Wall thickness tolerance, ovality, straightness and the permissible length deviation are all defined in the referenced product standard. Heavy-wall tube is usually supplied in the cold-drawn or hard temper because thick annealed walls tend to sag under their own weight; where soft temper heavy-wall tube is required, the standard states a wider straightness tolerance. All heavy-wall tube should be supplied with a mill test certificate reporting chemistry, tensile properties, flattening or expansion test results and any non-destructive examination carried out.
Manufacturing Route
Production starts with a cast billet or an extruded hollow shell. The shell is extruded or pierced, then cold drawn over a mandrel through a die that reduces diameter and wall simultaneously. Each drawing pass is followed by an anneal to remove work hardening; the number of passes is set by the total reduction required, which for heavy walls is considerably higher than for a thin-wall refrigeration tube. After the final draw, the tube is straightened, cut to length, stress-relieved where specified, pickled or bright-annealed, and finally inspected by eddy current, ultrasonic or hydrostatic test as the standard and the order require.
Applications of Heavy-Wall Tube
High-pressure hydraulic and pneumatic lines on presses, machine tools and mobile equipment, where brass tube combines pressure capability with easy flaring and brazing.
Heat exchangers and condensers with aggressive cooling water, where extra wall thickness provides a corrosion allowance over the design life.
Electrical bus tube and bus pipe in switchgear and substations, using high-conductivity copper in a wall thick enough for drilled and bolted joints.
Bearings, bushings and wear sleeves machined from C36000 or C26000 heavy-wall tube, exploiting the low friction of brass against steel.
Instrumentation and manifold fittings where the tube is threaded, grooved or compression-fitted directly.
Marine, desalination and offshore piping in the copper-alloy grades covered by ASTM B111.
Machining, Joining and Installation Notes
Free-cutting brass C36000 machines at high speed with light, well-broken chips and needs no special lubricant beyond a general-purpose cutting oil. Cartridge brass C26000 and muntz metal C28000 work-harden quickly and should be machined with sharp tooling, positive rake and a feed heavy enough to stay below the work-hardened layer. For copper heavy-wall tube, use high rake angles, generous coolant and light finishing passes.
Threading is normally done on brass; copper heavier than about 3 mm wall can also be threaded but the thread is weaker than the parent metal and should not be used as a structural joint. Brazing is the standard joining method for both families, with silver-based filler and a fluoride flux; welded joints are made on DHP copper where a fully metallic joint is required. Supports should be insulated or lined where brass contacts steel, to avoid galvanic attack in wet service.
Inspection and Common Pitfalls
Ordering errors cluster around three points. First, ordering copper when brass was intended, or the reverse, because both are described in quotation as "copper tube". Second, specifying wall thickness in gauge numbers for a product that is bought and inspected against metric or inch fractions. Third, assuming that all brass is equally machinable: C26000 and C36000 differ by a large factor in tool life, and the free-cutting grade should be specified explicitly when a machined part is required. On site, the common defects are cross-threaded joints, over-tightened compression fittings that split thin walls, and unprotected brass-to-steel contacts that corrode preferentially in damp conditions.
FAQ
Q: How do I decide between thick-walled copper tube and thick-walled brass tube?
Choose copper where thermal or electrical conductivity is the priority, and brass where strength, wear resistance or machinability matters more. Brass is also the lower-cost option for a given pressure duty.
Q: What copper content is normal in brass tube?
Cartridge brass C26000 contains 68.5–71.5 % copper, yellow brass C27000 contains 63.0–68.5 %, and muntz metal C28000 contains 59.0–63.0 %, with zinc making up the balance. The grade, not a single "60/40" figure, should be named on the order.
Q: Does thick wall thickness reduce corrosion?
It does not change the corrosion rate, but it provides the allowance that keeps the tube leak-tight for the design life once some wall has been consumed. It also resists erosion-corrosion at high flow velocities.
Q: Can heavy-wall copper tube be bent on site?
Only with a powered bender and a mandrel; the minimum bend radius for heavy walls is larger than for thin-wall tube, and the tube must usually be annealed locally before bending and stress-relieved afterwards.
Q: What tests should accompany a heavy-wall tube order?
A mill test certificate with chemical analysis, tensile and yield strength, elongation, flattening or expansion results, dimensional inspection and any eddy-current, ultrasonic or hydrostatic testing required by the product standard.
Q: Which temper is normal for thick-wall tube?
Cold-drawn or hard temper is standard because it holds a straight form and develops higher strength; annealed heavy-wall tube is supplied only on request and with wider straightness tolerances.
